As the computer industry has grown, numerous commercial software products have become available. It is now possible to buy “off-the-shelf” software for a variety of applications. However, off-the-shelf software has a significant drawback: it comes pre-configured to perform actions in a certain way—that is, it comes with a pre-determined “model” of the task that it is designed to perform. Unfortunately, computer users' needs do not always fit neatly into that model. Stated succinctly, when it comes to software, one size does not fit all.
For example, a user may purchase an off-the-shelf program to prepare invoices for a business. One of the functions performed by the program may be the computation of sales tax for the invoice, and the program may be designed with the understanding that the applicable tax rate is based on the state in which the sale occurred. The program, however, may be designed with the assumption a tax rate is uniform throughout a given state, and thus may be unable to compute sales tax in states where the tax rate varies by zip code. Moreover, since the program is delivered to the user as a self-contained, fixed set of instructions, there may be no way to add to the program the instructions that would compute the sales tax based on the zip code. In this case, the off-the-shelf program almost fits what the user needs to do, and yet the program is effectively unsuitable for the user's invoice needs, because the program's “model” of how to compute sales tax does not quite do what the user needs, and cannot be extended to do so. What is needed in this example is the ability to customize the off-the-shelf invoice program to compute sales tax according to whatever formula a user might need.
There are various solutions to the problem of customizing software, none of which are completely satisfactory. For example, it is common practice in the field of business software for the manufacturer of the software to rewrite a base program (e.g., an invoice program) to a customer's specifications. The customer's requirements are inserted into the source code by the manufacturer, the source code is recompiled, and a custom-built piece of software is delivered to the customer. This solution has the drawbacks that: (1) it is labor-intensive; and (2) there may be no consistency in the manner in which modifications to the original base program are performed, which makes it difficult to service and upgrade the custom-built programs.
Another solution is to use an interpretable script-type language for the application, in which case the source code is available to the user and customizations can be added as needed. Interpreted programs, however, are slower than compiled programs, and an interpreted program may not be able to meet the stringent performance requirements that apply in some circumstances.
Moreover, there do not currently exist any well-defined techniques or methods to customize applications that are built upon many “tiers” of machines and distributed via a loosely coupled, wide area network (typically the Internet). Prior systems that support some type of customization, such as Visual Basic for Applications (VBA), are most appropriate for desktop applications (such as the MICROSOFT EXCEL spreadsheet, or the MICROSOFT WORD word processor), and those techniques are not well suited for distributed applications.
In view of the foregoing, there is clearly a need for a system that overcomes the limitations and drawbacks of the prior art.